Whether you're a casual snapshooter or a professional photographer, you'll probably be in the market for flash memory cards sooner or later. Learn how to choose wisely from a deluge of sizes and models.
CompactFlash cards currently have capacities of up to 64GB, although the most popular cards sold are 8GB and smaller. Most cameras support any CF size up to 2GB, but to support cards 4GB and larger, the camera must support the the FAT32 file system. Contact your camera vendor if you aren't sure if your camera can use a 4GB or larger card. In some cases, a firmware upgrade might be necessary to enable the camera to use larger cards.
Oh, and with any flash memory card (CF or others), better format them using the camera's own Format feature. Formatting the card in a card reader can cause recognition problems, especially with larger cards.
The popular SD Card form factor supports sizes up to 2GB - but the lookalike SDHC form factor supports larger size. Which can you use? SDHC supports the FAT32 file system, so only devices that are specifically designed to use SDHC can use them. At least initially, SDHC support is limited to some high-end point and shoot and digital SLR cameras that also use SD media. See this technical brief from Lexar for details - or check with your camera vendor.
xD-Picture Card is used by Fujifilm and Olympus. When you shop for xD-Picture Card media, you will see some media marked Fujifilm and some marked Olympus. Does it matter? If you want to use the panorama feature available in some Olympus cameras (you can see a demonstration in my book Easy Digital Cameras), you must use Olympus-branded xD-Picture Card media.
You will also notice that some media is marked with an M next to the capacity, some with an H, and some with no marking at all. Type M and Type H cards use a different internal architecture than original xD-Picture cards to enable higher capacities (up to 2GB, compared to 512MB in the original versions). Type H cards are faster than Type M cards, and both are faster than original xD-Picture Card designs. See the Olympus xD-Picture Card Compatibility page or the Fujifilm xD-Picture Card and Adapters page to determine compatibility with specific camera models. Card readers designed for use with original xD-Picture Card media cannot read Type H or Type M cards.
Of the major flash memory families, the Sony Memory Stick family easily qualifies as the most diverse - and perhaps, the most confusing. The original blue Sony Memory Stick has long been superseded by Memory Stick Pro in standard or compact (Duo) sizes, along with High Speed Memory Stick Pro, Memory Stick PRO-HG, and variants made for consumer electronics: the PSP Memory Stick and Memory Stick Micro (M2).
Sony's Memory Stick Media Compatibility Information for Sony Digital Cameras page isn't the easiest to read either. Because most Memory Stick versions support MagicGate copyright protection (used for digital music) - a feature that matters on digital music players but not at all to digital camera users - you need to wade through a lot of verbiage. Let's make it simple: an X means you can't use the media in your camera, and O or C means you can use it (see the notes for MagicGate legalese) and the boldfaced number points you to the Remarks list (at the top of the page, not the bottom). Have fun!
What about memory card speed? That matters as well, but it's a topic we'll cover another time.